Ethylene and propylene are typical light olefins which are the most basic raw materials in the chemical engineering. In the domestic and foreign, the light olefins are mainly prepared from natural gas or light hydrocarbons by a steam splitting process in an ethylene combination unit. The second-largest source of light olefins is from a fluidized catalytic cracking (FCC) unit in a refinery. The conventional catalytic cracking process also produces light olefins as by-products with a yield of only less than 15% of feedstock during the production of gasoline and light diesels. Specific formulations of a catalytic cracking catalyst and/or adjuvant are usually selected in a refinery to improve the yield of propylene.
U.S. Pat. No. 5,670,037 discloses a process for producing light olefins, wherein the feedstock are petroleum fractions with different boiling ranges, residual oil or crude oil. A solid acidic catalyst is used in a fluidized bed or moving bed reactor to conduct the catalytic conversion reaction, at a temperature of 480° C. to 680° C. and a pressure of 0.12 to 0.40 MPa, with a reaction time of 0.1 to 6 seconds and a weight ratio of catalyst to oil of 4-12, and the spent catalyst is stripped, burnt and regenerated, then recycled to the reactor for reuse. Compared to the conventional catalytic cracking and the steam splitting process, the process can give more propylene and butylene, wherein the total yield of butylene and propylene can reach at about 40%.
U.S. Pat. No. 6,538,169 discloses a process for improving the yield of light olefins, which comprises, recycling a part of the spent catalysts back to the bottom of the reactor, raising the catalyst to oil ratio, decreasing the temperature at which the catalyst and the oil contact, and adding a ZSM-5 adjuvant to the reaction system.
U.S. Pat. No. 6,791,002B1 discloses a riser system for cracking of hydrocarbons, wherein the cracking reaction temperature and residence time of feedstock having different compositions are controlled to improve the yield of the light olefins. The process didn't mention to optimize the conversion of components by modifying the active components of the catalyst in order to improve the selectivity of the light olefins.
The catalytic cracking process for obtaining light olefins from petroleum hydrocarbons have been reported in many patents. The metal-supported catalysts are used, wherein the carrier are SiO2, Al2O3, or other oxides, and the metal components are mainly selected from elements of Groups IIB, VB, VIIB, and VIII, which show a hydrogenation or dehydrogenation activity, exhibits a dehydrogenation activity in cracking conditions of high temperature and low pressure, and thus accelerates the production of light olefins (U.S. Pat. No. 3,541,179, U.S. Pat. No. 3,647,682, DD225135 and SU 1214726). When these catalysts are used, owing to the dehydrogenation property of the supported metals, the coke formation due to the polymerization reaction is accordingly accelerated during the cracking reaction, and increased coke is formed on the catalyst. Hence, only these light feedstocks with a boiling range less than 220° C. can be used.
A composite oxide catalyst is used in some other patents. By ways of example of these catalysts, mention will be made of a catalyst comprising ZrO2, HfO2 as main components, Al2O3, Cr2O3, MnO, Fe2O3 and oxides of alkaline metal or alkaline earth metal as an adjuvant (U.S. Pat. No. 3,725,495, U.S. Pat. No. 3,839,485); and SiO2.Al2O3 catalyst containing small amounts of Fe2O3, TiO2, CaO, MgO, Na2O, and K2O (SU 550173, SU 559946).
With the widespread application of zeolite in the petrochemical and petroleum processing, there appears the third class of catalysts, i.e., the catalysts comprising zeolite. In recent years, a shape selective additive is added into a catalyst to enhance the octane number of catalytic gasoline. For example, U.S. Pat. No. 3,758,403 discloses a catalyst using ZSM-5 zeolite and a large pore zeolite (with a ratio of 1:10 to 3:1) as active components, and in addition to enhancing the octane number of the gasoline, this catalyst provides a higher yield of C3 and C4 olefins, with a C3 and C4 olefins yield of roughly 10% by weight.
When the catalyst contains a mixture of a zeolite with the MFI structure (silicon-rich five-member-ring zeolite) and a zeolite with a pore size greater than 7 angstrom is used in the cracking of petroleum hydrocarbons to produce light olefins, the large pore zeolite (Y type zeolite mainly) is used to crack the feedstock to produce gasoline and diesel, which are further cracked into light olefins by the zeolite with the MFI structure (U.S. Pat. No. 3,758,403, CN 1043520A, U.S. Pat. No. 500,649, and CN 1026242C). To increase the olefin selectivity of catalysts, the MFI zeolite is further modified with, for examples, transition metals (U.S. Pat. No. 5,236,880), phosphorus (CN 1205307A, U.S. Pat. No. 6,566,293), rare earth (CN 1085825A), phosphorus and rare earth (CN 1093101A, U.S. Pat. No. 5,380,690, CN 1114916A, CN 1117518A, CN 1143666A), phosphorus and alkaline earth metals (CN 1221015A, U.S. Pat. No. 6,342,153, CN 1222558A, U.S. Pat. No. 6,211,104), and phosphorus and transition metals (CN 1504540A).
The zeolite beta has a 12 member-ring structure with intersected porous channels, wherein the pore diameter of the 12-member ring is 0.75-0.57 nm for the one-dimension porous channel parallel to the (001) crystal face, while the pore diameter of the 12 member-ring is 0.65-0.56 nm for the two-dimension porous channel parallel to the (100) crystal face. The zeolite beta is a silicon-rich large pore zeolite having a three-dimension structure that is the only one discovered up to now, and has both acid catalytic property and structural selectivity due to its structural particularity, and further has very high thermostability (the failure temperature of the crystal lattice is higher than 1200° C.), hydrothermal stability and abrasion-resistant property. Due to the unique structural feature, the zeolite beta has good thermal and hydrothermal stability, acid resistance, anti-coking property and catalytic activity in a series of catalytic reactions; therefore it has been developed rapidly into a new-type of catalytic materials in recent years. Many uses of the zeolite beta in the cracking of petroleum hydrocarbons to produce light olefins are reported.
CN 1103105A discloses a cracking catalyst being capable of giving a higher yield of isobutylene and isoamylene, and said catalyst is a composite consisting of four active components and a carrier, wherein the active components consist of a modified HZSM-5 and silicon-rich HZSM-5 with different silica/alumina ratios, USY and zeolite beta, the carrier consists of a natural clay and an inorganic oxide, and the components and contents of the catalyst are as follows: (1) the modified HZSM-5 with a silica/alumina ratio of 20 to 100: 5-25% by weight; (2) the silicon-rich HZSM-5 with a silica/alumina ratio of 250 to 450:1-5% by weight; (3) the USY zeolite: 5-20% by weight; (4) the zeolite beta: 1-5% by weight; (5) the natural clay: 30-60% by weight; (6) the inorganic oxide: 15-30% by weight. The catalyst has the feature of being capable to give a higher yield of isobutylene and isoamylene, while can co-produce a gasoline with a high octane number.
CN 1057408A discloses a cracking catalyst containing a silicon-rich zeolite, wherein said catalyst consists of 10-30 wt % of modified silicon-rich zeolite and 70-90 wt % of carrier, said modified silicon-rich zeolite comprises, based on the weight of the zeolite, 0.01-3.0 wt % phosphorus, 0.01-1.0 wt % of iron or 0.01-10 wt % of aluminum (the aluminum in the structure of the zeolite is excluded), and is selected from mordenite, zeolite beta, or ZSM zeolite with a silica/alumina ratio higher than 15, and said carrier is an inorganic oxide or a mixture of an inorganic oxide and kaolin. The catalyst is used to produce light olefins during the catalytic cracking process of hydrocarbons, and co-produce gasoline and diesel.
CN 1099788A discloses a cracking catalyst being capable of giving a higher yield of C3-C5 olefins, wherein said catalyst consists of 10-50 wt % of Y type zeolite with a unit cell size of 2.450 nm or less, 2-40 wt % of a zeolite selected from ZSM-5 zeolite or zeolite beta modified with P, RE, Ca, Mg, H, Al, etc. and mixture thereof, 20-80 wt % of semi-synthetic carrier consisting of kaolin and alumina binder. Said catalyst can enhance the yield of C3-C5 olefins wherein yield of iC4=+iC5= is Up to 10-13 wt %, simultaneously keeping the yield of gasoline at about 35-42 wt %.
CN 1145396A discloses a cracking catalyst being capable of giving a higher yield of isobutylene and isoamylene, and said catalyst consists of three active zeolite components and a carrier, based on the weight of the catalyst: 6-30 wt % of silicon-rich five-member-ring zeolite containing phosphorus and rare earth, 5-25 wt % of USY zeolite, 1-5 wt % of zeolite beta, 30-60 wt % of clay, and 15-30 wt % of inorganic oxide. The catalyst has the feature of being capable to give a higher yield of isobutylene and isoamylene, while can co-produce a gasoline with a high octane number.
CN 1354224A discloses a catalytic cracking catalyst for producing a gasoline rich in isomeric alkane, propylene and isobutane, wherein said catalyst consists of, based on the weight of the catalyst, 0-70 wt % of clay, 5-90 wt % of inorganic oxide and 1-50 wt % of a zeolite. The zeolite is a mixture of, based on the weight of the zeolite, (1) 20-75 wt % of silicon-rich Y-type zeolite with a silica/alumina ratio of 5-15 and RE2O3 content of 8-20 wt %, (2) 20-75 wt % of silicon-rich Y-type zeolite with a silica/alumina ratio of 16-50 and RE2O3 content of 2-7 wt %, and (3) 1-50 wt % of zeolite beta or mordenite or ZRP zeolite. The catalyst can increase the content of the isomeric alkane in the gasoline and simultaneously increase the yield of propylene and isobutane, but the yield of propylene is just slightly enhanced.
CN 1504541A discloses a catalyst for catalyzing the cracking of hydrocarbons to produce light olefins and co-produce aromatics, comprising a molecular sieve with a pore size of 0.45-0.7 nm, an amorphous oxide and at least two modifying components selected from phosphorus, alkaline earth metals, lithium, and rare earth. Said molecular sieve is a silica-alumina or silica-phosphor-alumina molecular sieve, wherein said silica-alumina molecular sieve is ZSM-5, ZSM-11, mordenite, or zeolite beta, and said silica-phosphor-alumina molecular sieve is SAPO-5, SAPO-11 or SAPO-34. The active center of the catalyst can be modulated according to the practical needs of products, to prepare the light olefins as main products or co-produce the aromatics during the production of olefins.
CN 1566275A discloses a molecular sieve-containing catalyst for cracking hydrocarbons and preparation thereof, said catalyst contains a molecular sieve which is a mixture of a first zeolite and a second zeolite, a thermotolerant inorganic oxide and a metal component with or without clay, the first zeolite is a Y-type one, the second zeolite is one with a molar ratio of silica to alumina of more than 20, the content of the first zeolite is 1-50 wt %, the content of the second zeolite is 1-60 wt %, the content of the thermotolerant inorganic oxide is 2-80 wt %, the content of the clay is 0-80 wt %, the content of the metal component is 0.1-30 wt %, and said metal components substantially exists as a reduction valence state. The catalyst can not only give a high yield of C3-C5 olefins, but also have a higher activity of desulfurization, and further have a higher cracking activity. Said second zeolite is one or more selected from zeolite with MFI structure containing phosphorus, rare earth and/or alkaline earth metal or not, zeolite beta containing phosphorus, rare earth and/or alkaline earth metal or not, mordenite containing phosphorus, rare earth and/or alkaline earth metal or not.
U.S. Pat. No. 5,006,497 and U.S. Pat. No. 5,055,176 disclose a multi-component catalyst and the catalytic cracking process thereof. Said catalyst comprises a matrix, a large pore molecular sieve, a paraffin cracking/isomerization molecular sieve and an aromatization molecular sieve, wherein said large pore molecular sieve is selected from the group consisting of zeolite Y, DeAlY, USY, UHPY, VPI-5, columnar clay, SAPO-37, zeolite beta and mixtures thereof; said paraffin cracking/isomerization molecular sieve is selected from the group consisting of hydrogen-type ZSM-5, ZSM-11, ZSM-22, ZSM-35 and ZSM-57; and said aromatization molecular sieve is GaZSM-5.
US 20050070422 discloses a catalyst composition used for increasing the yield of propylene by catalytic cracking, wherein said catalyst comprises a first molecular sieve having an intermediate pore size, a second molecular sieve having at least one pore size of the channel which is less than that of the first molecular sieve, and optionally a third large pore molecular sieve, wherein said first molecular sieve is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-57, ITQ-13 and MCM-22; the second molecular sieve is selected from the group consisting of ECR-42, ZSM-22, ZSM-35, ZSM-23, MCM-22, MCM-49, SAPO-11, SAPO-34 and SAPO-41; and the third molecular sieve is selected from the group consisting of faujasite, zeolite L, VPI-5, SAPO-37, zeolite X, zeolite beta, ZSM-3, ZSM-4, ZSM-18, ZSM-20, MCM-9, MCM-41, MCM-41S, MCM-48, Y-type zeolite, USY, REY, REUSY and so on. Said catalyst is suitably used for the production of propylene by cracking naphtha and heavy hydrocarbon feedstocks.
With further increasing demand on light olefins, a process for the catalytic conversion of hydrocarbons is desired to be developed, wherein said process exhibits a higher ability to convert petroleum hydrocarbon and higher yield for light olefins, especially propylene.